Since excellent throttle response is regarded as important for a two-wheeled vehicle, compared with that for a four-wheeled vehicle, there is sometimes a case where a multiple throttle device is employed as a throttle device to regulate intake air to an engine in response to throttle operation of a driver. In such a multiple throttle device, there is taken a configuration in which intake passages are defined in a throttle body correspondingly to individual cylinders of the engine, throttle valves are disposed in the individual intake passages and supported on a throttle shaft, and the throttle shaft is driven and rotated in response to the throttle operation to synchronously open and close the throttle valves.
Moreover, since many engines mounted on two-wheeled vehicles have high speed rotation-type characteristics and require more precise and appropriate throttle opening adjustment, throttle devices are electronically controlled in recent years. In such a multiple throttle device which is electronically controlled (hereinafter referred to simply as electronically controlled throttle device), the throttle shaft is driven and rotated with a motor via a gear train of a gear unit to open and close the throttle valves. Twist of the throttle shaft in driving and rotating leads to phase displacements of the throttle valves, and eventually, differences in intake air amounts. Hence, the twist of the throttle shaft is suppressed by inputting driving force from the motor to the middle of the throttle shaft in the longitudinal direction.
FIG. 5 is a cross-sectional plan view showing an electronically controlled throttle device of the conventional art as above. FIG. 6 is a partially expanded cross-sectional plan view of the periphery of a gear unit of the same. An electronically controlled throttle device 31 in this example is a quadruple throttle device for a 4-cylinder engine, and its throttle body is divided into a first throttle body 2 and a second throttle body 3, which are connected to each other with not-shown bolts.
A pair of intake passages 5#1 and 5#2 that respectively correspond to a #1 cylinder and a #2 cylinder of an engine are defined in the first throttle body 2, and a pair of intake passages 5#3 and 5#4 that respectively correspond to a #3 cylinder and a #4 cylinder of the engine are defined in the second throttle body 3. A not-shown air cleaner is connected to the intake passages 5#1 to 5#4 on the opposite engine side, and moreover, fuel injection valves 6 show their tips inside the individual intake passages 5#1 to 5#4.
One throttle shaft 8 is rotatably supported in the first and second throttle bodies 2 and 3 so as to penetrate the intake passages 5#1 to 5#4, and throttle valves 10 disposed in the individual intake passages 5#1 to 5#4 are supported on the throttle shaft 8. A gear unit 12 is disposed between the first and second throttle bodies 2 and 3, and a not-shown motor is connected to the gear unit 12. Driving force from the motor is transmitted to the throttle shaft 8 via a gear train 14 built in the gear unit 12, and drives and rotates the throttle shaft 8 to synchronously open and close the throttle valves 10.
Cylindrical spigots 17 are formed at the end parts of the individual intake passages 5#1 to 5#4 on the engine side, the end parts of rubber joints 18 extending from individual intake ports of the engine are respectively fitted to the spigots 17, and they are fastened and fixed thereto with hose bands 19 or the like. Intake air introduced from the air cleaner into the intake passages 5#1 to 5#4 is mixed with fuel injected from the fuel injection valves 6 while being regulated in its flow rate in response to the degree of throttle opening, and is introduced into the cylinders through the rubber joints 18 and the intake ports of the engine to serve combustion.
A space for fitting the end part of the rubber joint 18 (hereinafter referred to as attachment space of the rubber joint 18) is needed in the periphery of each spigot 17. However, the gear unit 12 which the gear train 14 is built in occupies a significant region in the radial direction with the throttle shaft 8 being as the center. Hence, a part thereof interferes with the spigots 17, which prevents the attachment spaces of the rubber joints 18 from being secured.
Therefore, as shown in FIG. 6, in the electronically controlled throttle device 31 of the conventional art, the total lengths L2 of the throttle bodies 2 and 3 along the intake air flowing direction are elongated to displace the positions of the spigots 17 to the engine side (separate them from the gear unit 12 by a dimension l3), and thereby, the interference with a part of the gear unit 12 is prevented to secure the attachment spaces of the rubber joints 18.
Meanwhile, as such a throttle device in which the throttle body is divided, for example, a technology in Patent Document 1 is proposed. The throttle device in Patent Document 1 employs conventional wire drive, and therein, a connection synchronization mechanism is provided between both throttle bodies. Throttle operation by the driver is transmitted to a throttle shaft of one throttle body via a wire, the rotation of the throttle shaft is transmitted to a throttle shaft of the other throttle body via the connection synchronization mechanism, and the connection synchronization mechanism enables a phase between the throttle shafts to be finely adjusted. Further, in this throttle device, in order to improve flexibility in designing the connection synchronization mechanism, spigots of a pair of intake passages positioned on both sides of the connection synchronization mechanism are formed to have eccentricity downward by a and formed to have eccentricity in a direction away from each other by b.